Add support for callIfNull

src/compose-rules.js

@@ -17,61 +17,85 @@ module.exports.compose = function composeValidators(validators) {
 	let isRequired = validators.some((rule) => isRequiredMarker(rule));
 	let nonMarkerRules = validators.filter((rule) => !isRequiredMarker(rule));
 
+	function callRule({ rule, value, context }) {
+		try {
+			let result = isCombinator(rule)
+				? rule.callback(value, applyValidators, context)
+				: rule(value, context);
+
+			if (result !== undefined) {
+				if (isValidationResult(result)) {
+					if (Array.isArray(result.errors)) {
+						let nonValidationErrors = result.errors.filter((error) => !matchValidationError(error));
+
+						if (nonValidationErrors.length === 0) {
+							return {
+								errors: result.errors,
+								newValue: result.newValue
+							};
+						} else {
+							// We should never reach this point, but it could possibly occur if someone erroneously includes non-ValidationError errors in a validationResult. Note that this is a last-ditch handler, and so we only throw the first non-ValidationError error and let the user sort out the rest, if any.
+							throw nonValidationErrors[0];
+						}
+					} else {
+						throw new Error(`The 'errors' in a validationResult must be an array`);
+					}
+				} else if (result instanceof Error) {
+					// We could interpret returned Errors as either values or a throw substitute. Let's wait for users to file issues, so that we know what people *actually* need here.
+					throw new Error(`It is currently not allowed to return an Error object from a validator. If you have a reason to need this, please file a bug!`);
+				} else {
+					return {
+						errors: [],
+						newValue: result
+					};
+				}
+			} else {
+				return {
+					errors: [],
+					newValue: undefined
+				};
+			}
+		} catch (error) {
+			if (matchValidationError(error)) {
+				return {
+					errors: [ error ],
+					newValue: undefined
+				};
+			} else {
+				throw error;
+			}
+		}
+	}
+
 	return function composedValidator(value, context) {
 		if (isRequired && value == null) {
 			return validationResult({
 				errors: [ new ValidationError(`Required value is missing`) ],
 				newValue: value
 			});
-		} else if (value != null) {
+		} else {
 			let lastValue = value;
 
 			let errors = [];
 
 			for (let rule of nonMarkerRules) {
-				try {
-					let result = isCombinator(rule)
-						? rule.callback(lastValue, applyValidators, context)
-						: rule(lastValue, context);
-
-					if (result !== undefined) {
-						let transformedValue;
-
-						if (isValidationResult(result)) {
-							if (Array.isArray(result.errors)) {
-								let nonValidationErrors = result.errors.filter((error) => !matchValidationError(error));
-
-								if (nonValidationErrors.length === 0) {
-									errors = result.errors;
-									transformedValue = result.newValue;
-								} else {
-									// We should never reach this point, but it could possibly occur if someone erroneously includes non-ValidationError errors in a validationResult. Note that this is a last-ditch handler, and so we only throw the first non-ValidationError error and let the user sort out the rest, if any.
-									throw result.errors[0];
-								}
-							} else {
-								throw new Error(`The 'errors' in a validationResult must be an array`);
-							}
-						} else if (result instanceof Error) {
-							// We could interpret returned Errors as either values or a throw substitute. Let's wait for users to file issues, so that we know what people *actually* need here.
-							throw new Error(`It is currently not allowed to return an Error object from a validator. If you have a reason to need this, please file a bug!`);
-						} else {
-							transformedValue = result;
-						}
-
-						if (transformedValue != null) {
-							lastValue = transformedValue;
-						}
+				if (value != null || rule.callIfNull === true) {
+					let result = callRule({
+						rule: rule,
+						value: lastValue,
+						context: context
+					});
+					
+					if (result.newValue != null) {
+						lastValue = result.newValue;
 					}
-				} catch (error) {
-					if (matchValidationError(error)) {
-						errors = [ error ];
-					} else {
-						throw error;
+					
+					if (result.errors.length > 0) {
+						errors = result.errors;
+						break;
 					}
-				}
-
-				if (errors.length > 0) {
-					break;
+				} else {
+					continue;
 				}
 			}
 
@@ -82,8 +106,6 @@ module.exports.compose = function composeValidators(validators) {
 					? lastValue
 					: undefined
 			});
-		} else {
-			return validationResult({ newValue: undefined });
 		}
 	};
 };